Electric smelting of zinc ore



Jan. 14, 1930. E. c. GASKILL ELECTRIC SMELTING OF ZINC ORE Filed Nov.17. 192

INVENTQR. By 224 M Mx% ATTORNEY. My

Patented Jan. 14, 1930 UNITED STATES PATENT OFFICE EARL C(GASKILIL, REDB ANK, NEW JERSEY, ASSIGNOB T0 ST. JOSEPH LEAD COMPANY, OE YORK, N. Y.,A CORPORATION OF NEW YORK ELEQTRIC SMELTING or'zmc o'er:

Application m r November-17, 1920. SeriaLNo. 148,801.

v This invention relates generally to the electric smelting of zinc oreand more particularly to a method for producing zinc or zinc oxide bythe reduction of loose ore in a furnace of the electric resistor type.-

So far as I am aware, no practical method of electric smelting of zincores has been heretofore developed.

It is a general object of the present invention to provide a process ormethod for electrically smelting zinc ore in a furnace of the electricresistor type, and by continuous, as

distinguished from batch, operations.

.The apparatus required for carrying out the process, includes, as itsmost important element, a furnace structure of the vertical shaft,electric resistor type. The furnace is formed of suitablerefractorymaterials and provided with annular electrodes formed of graphite, orother suitable material, mounted at the upper'and lower ends of thereducing.

[zone of the furnace. The electrodes are massive in construction and theopenlngs therethrough register with the furnace bore or chamber so thatthe charge in the chamber ripheri'es thereof. The upper extremity of thefurnace is sealed, 1n operation, against the-ingress of air or theescape of gases.

Avfeature of the invention resides in the preheating of material to betreatedin two stages. In the first stage the material is heated to atemperature of approximately 600 C. to drive off moisture. Thematerialis then charged into a second preheater forming part of the furnacestructure in which the temperature of the material is raised to 900, or1000 C., or the reducing temperature, in order to economize current inthe reducing operation.

I'have found that the smelting of zinc ore in a furnace ofthe electricresistor type can be considerably facilitated by sintering the orebefore subjecting it to the reducing operation, although the reductionof the ore can be obtained without the preliminary sintering, ifnecessary. The sintering of the ore may be achieved as a part orextension of the roasting operation to which zinc ores, and particularlyores of the sulphide type, are subjected. The'sintering efiect can beobtained by a local intensification of the application of heat to theore as it passes through the roaster. The sintering action is greatlyfacilitated by the presence of iron contained in many zinc ores, andwhich may be added, if desired, as an aid to the sintering action,although the sintering effect can be obtained in other ways.

A sintered condition of the ore charged into the furnace contributes tothe success of the smelting operationin that the charge is in a goodmechanical condition to flow down the shaft without clogging or jammingand, in addition, possesses a porous structure which aids in heating thecharge through the impermeation of the material by the hot gases evolvedin the reducing operation. The porous nature of the sinteredchargegreatly facilitates the free passage therethrough of gases andvapors resulting from the reduction reactions and thereby assists intheir removal from the furnace chamber. Another advantageous feature ofthe use of sintered material resides in the fact that sintered ore,unlike ore that has not been sintered, when heated, becomes a relativelygood conductor of electricity and, thereby facilitates the passingofcurrent through the charge to effect the reducing operation.

It has been statedthat the presence of iron in the ore facilitates thesintering operation. I have foundthe iron to be useful in other respectswhich aid substantially in the reducing of theore. In the application ofheat to the sintered-material in the upper part of the furnace metalliciron is liberated and still further increases the conductive propertiesof the material. The liberated iron also aids in the reduction of thezinc ore and apparently possesses a chemical activity or instabilitywhich results. in the taking up by the iron of the oxygen combined withthe zinc so that zinc is set free.

, In the operation of a furnace in which the process can be-carried outthe mass of heated and sintered ore which is passed into the furnacechamber between the electrodes is sufficiently conductive to provide apath of the flow of current between the electrodes while, at the sametime, offering suflicient resistance to the flow of current to roducethe in-. crease in temperature required to liberate zinc from the ore.The reducing operation has been found to take place with much greaterrapidit under the conditions named than in the o d retort practice.sults, in part, because the electrical resistance of the charge is verymuch less than the thermal resistance. The efficiency of the operationis much higher than that of the retort practice, in part because theinternal application of heat through the action of the electric currentis much more eflective than is the external application of heat whichmust penetrate through the thermally non-0onductive material.

I have found also that the efficiency of operation of the furnace isconsiderably increased by a reducing effect produced by the action ofthe electric current itself. In other words a reducing action isachieved which is greater than could be expected from the moderatetemperatures existing in the smelting zone between the electrodes. Theaction of the current is believed to produce an ionization effect whichfacilitates the setting free of the zinc and directly convertingelectrical into chemical ener y.

This electrical e ect is so pronounced that if, when the-furnace hasbeen operating at approximately 200 volts, with a pyrometric indicationthatthe temperature conditions are suflieiently high for satisfactoryreduction and with a liberal flow 'of zinc va or issuing from thefurnace, the voltage 'e increased" to 400 without changing otherconditions, the increased voltage causes the power input to be more thandoubled with a proportionate increase inthe amount of vapor liberated.These changes in the power input and the amount of vapor roduced areaccompanied by an astonishing lowering of the furnace temperature,thereby indicating that at or over certain critical potentials reductiontakes place at lowered temperatures with an increase in simplicity andefiiciency of the reducing operation.

In operations conducted in a furnace of the type described it has beenfound that in no partof the reducing chamber of the furnace does thereexist a higher temperature than the optimum temperature known to beneeded for the purpose of reduction of the ore. There exists no hotspots in the reducing chamber and the control and selection of uniformtemperatures suitable for the pur ose is readily efi'ected. Theuniformity an efficiency of temperature produced results in part throughthe upward passage throu h the descending massof material in the reucing zone of hot gases which imper'mea te and heat all portions of theporouslmass of material constituting the charge.

amaaaa This re-.

In the drawing a single, diagrammatic v1ew has been provided toillustrate an em-.

bodiment of means for carrying out the process.

Referrin to the drawing for a more detailed description of theinvention, a vertical shaft furnace is shown at 10 in which thetemperature required for the smelting or the reduction of the ore isprovided by way of two annular electrodes 11 and 12 which are mounted inthe wall of the furnace at the upper and lower ends of the reducin zonethereof. The walls of the furnace are formed of any suitable heatrefractory material and are provided at vertically separated intervalswith annular overhanging portions 13 which serve to provide spaces freefrom solid material and from which vapors evolved in the reducingaction. can be freely drawn by means of tuyere openings 14 terminatingin the grooves or recesses 15 beneath the overhanging shoulders 13. Withthis construction, the clog ing of the tuyere openings or passages by te solid matenal of the charge can nottake place and the passage ofvapors through the openings is insured.

In order to prevent the access of air to the interior of the furnacechamber 16, a hinged closure member 17 is provided at the upper end ofthe furnace shaft-which is normally kept closed in operation whileproviding means for gaining access to the interior of the furnace forany purpose.

A preheatingdevice 18 is provided into which the material to be treatedis delivered by means of a conveyor 19. By means of oil or gas burners,the charge present in the preheater 18 is brought up to a temperaturesuch as will drive off all the moisture content of the material in thechamber of the preheater.

A temperature of approximately 690 C. is

approporiate for this purpose and this temperature is not so high as toinjure the material of which the preheater and adjacent parts areformed.

From the preheater 18 a valve or gate 20 operates to feed materialthrough the inclined passageway 21 into the upper end 22 of the furnace.The hot material in a thorough 1y dry condition and free of Water vaporthen finds its way into the chamber of a preheating unit 23 in which thetemperature is brought u to a higher point ap roximating that at W ichthe reduction of the charge takes place through the action of currentsupplied through the electrodes 11 and 12. A

good temperature, suitable for the purpose, approximates 1000 C. and theproduction of this temperature by means of the consumption of oil or gasas fuel in the preheater 23 serves to initiate the reduction of any ironoxide present in the ore as well as to economize in the consumption ofelectric current in the reducing operation.

The feeding device 20 is preferably automatically operated through acontrol exer cised by the level of the material in the furnace so that acolumn of material is continuously maintained in bridging relation tothe electrodes 11 and 12, thereby producing continuous as distinguishedfrom batch operations.

From the smelting zone ofthe furnace, which extends between theelectrodes 11 and 12, the tuyere passages lead into condensers 24 inwhich the zinc vapor is condensed to liquid, or to a vertical pipe 25through which the vapors and air are drawn and burned at the port 50 asa result of the action of a blower 26 and thence pass through aseparator 27 into a bag room 28 in which bags 29 are suspended for thecollection of the oxide dust'in a known manner. It will thus be seenthat in the same operation both the metallic or spelterform of the zincmay be ob. tained and the oxide form so that either or both the ultimateproducts may be obtained in the-operation of the apparatus described.

It will be seen that the condensers-24 are mounted at differentelevations or levels along the side wall of the furnace 10. By thismethod of condensing I am enabled to obtain different varieties ofdifferent types of spelter or metallic zinc. denser there will beobtained zinc having cadmium intermixed therewith. In the lowercondenser 24 zinc having lead intermixed therewith will be obtained. Incondensing vapors in the tuyere openings be tween the uppermost and thelowermost condensers illustrated, a substantially pure formconductivityin the mass of material to en-.

able current to flow through the column of material between theelectrodes, carbon in the .form of coke, coal or the like, is intermixedwith the charge before it is fed into thefurnace. I may make use also ofthe iron content of the ore for this purpose andthereby reduce to aconsiderable extent the proportion of carbonaceous material used forthis purpose. I contemplate the elimination of carbon for addingconductivity and making use only of so much carbon as is needed in thereducing operation.

I have-found that the use of iron, in addition to adding to theelectrical conductivity of the charge, is a useful agent in bringingabout the reduction of'the charge. In exer- In the uppermost con-''c'ising this function, iron oxide is apparently reduced in the secondreheater 23 as well as in the upper part of t e smelting zone adjacentthe upper electrode 11. The liberated iron, which is in solid form, asit travels downwardly through the reducing zone, apparently produces anionization or chemical instability which results in the taking up by theiron of oxygen from the zinc oxide compounds contained in the ore withthe result that zinc is set free through the presence'of the iron aswell as through the reducing action of the carbon monoxide producedthrough the action of the heating current on a carbonaceous materialadmixed with the charge. The use of iron therefore has a twofold actionwithin the furnace in that it adds to the conductivity of the charge andin addition it facilitates the reducing action.

I have found that the action of electric current on a charge containedin a furna ce of the type described produces a reducing action onthecharge which is substantially greater than could be expected from thetemperatures attained in the smeltin zone" between the electrodes. Ihave found that through a considerable range the voltage of current supplied to the electrodes can be increasedwith-' out bringing about acorresponding increase in temperature within the furnace. On thecontrary, I have found that an actual drop in temperature follows theincrease of voltage of the current up to a pointcfound most effective orefiicient by actual trial; When this condition is attained, it'has beenfound that a greater increase in the amount of material reduced isobtained than can be measured by the increase of voltage of the currentsupplied to the furnace. This increase in the quantity of materialproduced by the operation of the furnace with an actual drop in thetemperatures attained within thefurnace chamber indicates that theaction of the current does something more than merely zinc compoundswith an ionization effect which results in or facilitates the reductionof the ore and the liberating of the zinc. In other words, under theconditions named, there appears to be a direct conversion of theelectrical into chemical energy withoutan intermediate conversion ofelectrical energy into heat followed by a conversion ofheat intochemical energy.

By reason of the assistance providedby the iron in bringing about thereduction of the zinc compounds and also through the part which theelectric current itself. plays in the reducing operation, the reducingaction takes place in a furnace of the type described at a considerablylower temperature than has heretofore been found necessary for furnacewhich takes the form of a cooling cylinder 31 through which the spentcharge or residue passes from the furnace chamber. The lower extremityofthe cooling tube 31 terminates in a water seal provided in a bowl-vshaped member 32 which is rotated on a shaft 33 in such manner that astationary plow or scraper 34 directs material from the bowl 32 onto aconveyor 35 leading to a suitable discharge point. Water is provided forthe water seal through a pi e 36 and an overflow 37 in the bowl 32directs water into an annular trough-shaped member 38 from which it isconveyed to a Waste connection.

A feature of the invention resides in. the

preliminary treatment of the ore before it is charged into the reducingfurnace 10.v I

' have found that reducing operations in a furnace of the type describedare greatly facilitated if the ore charged into the furnace is incontent of the ore facilitate the wind box member.

a sintered form. The sintering of the ore can be produced simultaneouslyor in supplement to a roasting operation on a machine of the type shownat 39 in the drawing. This machine includes a ho per 40 in which thematerial is placed an from which it is delivered to a series of pans 41havin perforated bottoms and arranged to travel horizontally over a windbox structure 42 connected by means of a ipe 43 with any suitable sourceof exhaust. 11 oil burner 44 is placed at the point of delivery of thematerial from the hopper 40 to the receptacles 41 and serves to ignitethe sulphur ordinarily present in the ore.- When once ignited, thematerial is subjected to the desired roasting and sintering action byreason of the burnin of the sulphur d by the vigorous down draftprovided by the wind box struc- :ure throu h the relatively thin layersof material passmg along the open upper face of The desirable sinteredcondition of the ore which is obtained from the apparatus shown at 39may be produced with various ores through the use of a sufiicientintensity of heat. However, I find ductor of'electricity while roasted'sinter is a -is excluded an Y\ Y; relatively good conductor. Thesinteredore not onl assists in the conductivity of the charge at themechanical condition of the sinter facilitates the free flowing of thecharge downwardly through the bore of the furnace. The reduction of theiron oxide near the upper part of the furnace leaves the metallic ironin a anular condition resembling sand and it willbe seen that thisphysical structure faciltates the flowing action referred to. Thematerial thus roasted and brought to the desired condition of sinter isdelivered from the end of the machine 39 ceous material is deliveredfrom the mixture 48 into hopper or boo tr49of the conveyor 19 fordelivery into the p'reheater 18 of the furnace structure.

It will thus be seen that I have provided a method for the reduction ofzinc ores in a furnace of a shaft type to which the access of air areducing atmosphere is maintained. The charge in the furnace chamber iscontinuously renewed as fast as it is lowered in the reducing operationso that the uniform temperature which is necessary for the carrying outof a reducing operation without the formation of blue powder isachieved. In addition, the preparation of the furnace facilitates thereduction of ore in nace chamber before the material passes into thereducing zone adds still further to the effectiveness of the process.The use of iron as a part of the natural content of the ore or as aningredient added thereto before reduction aids in the carrying out ofthe reducing operation. The control of current in such manner that themaximum production of liberated metal is obtained while at the same timean actual lowering of the temperature reduction takes place is adistinct achievement in the new process of ore reduction described. Theproduction of spelter or metallic zinc and also of zinc oxide in thesame furnace as well as the production of spelter of different grades isanother advantage of the process set forth. In addition, the productionof zinc oxide in connection with a sealed type of electric resistorfurnace results in the formation of zinc oxide of a superior quality ascom pared with zinc oxide hertofore produced by known processes.

What I claim is:

1. The process for smelting zinc ore which comprises sintering the oreto make the body of the ore more porous and more conductive v in thereducing operation then in mlxlng carbonaceou material with the sinteredore, and then in passing electric current through the mixture to reducethe ore and liberate the 2. The process of reducing zinc ore 'whichcomprises feeding aloose mixture of sintered zinc ore and carbonaceousmaterial in a vertical column between spaced electrodes, whereby thecharge forms a resistance between the electrodes, passing an electriccurrent therethrough to heat and reduce the ore and vaporize the zinc,withdrawing the spent material from the lower end of the column andremoving the zinc vapor.

3. The process as claimed in claim 2 in which the charge is preheatedbefore-passing it between the electrodes.

4. The process of reducing zinc ore which comprises feeding a loosemixture of zinc ore and carbonaceous material in a vertical col umnbetween spaced electrodes, whereby the charge forms a resistance betweenthe-electrodes, passing an electric current therethrough to heat andreduce the ore and vapor- 'ize the zinc without substantial slagging .or

fusion of the charge, withdrawing the spent materialfrom the lower endof the column and removing the zinc vapor.

) EARL c. GASKILL.

